The owner of the Daily Telegraph is understood to have called in private investigative firm Kroll to discover who at the newspaper leaked Vince Cable's comments about Rupert Murdoch to the BBC after it decided not to publish them.

Cable told two undercover Daily Telegraph reporters last year he had "declared war" on the media mogul by referring his offer to buy out BSkyB to the media regulator Ofcom.

The paper published other comments made by Cable on 20 December, but omitted his quotes about Murdoch from its report.

Those remarks were picked up by the BBC's business editor, Robert Peston, and published on his blog.

Cable was subsequently stripped of his powers to block media mergers by David Cameron, and they were handed to the culture secretary, Jeremy Hunt.

It is understood that four employees from the secretive corporate investigators Kroll have began interviewing Daily Telegraph staff, starting with members of the IT department.

The circumstances surrounding the leak have been the subject of intense speculation. Some industry insiders alleged that the Telegraph chose not to publish Cable's comments about Murdoch because it believed it would lead to his sacking as business secretary, removing a potentially serious obstacle to Sky's efforts to buy out BSkyB.

Telegraph Media Group, which also owns the paper's Sunday sister title and the Spectator, is a member of an alliance of media groups which is opposed to News Corp's bid to take full control of BSkyB.

The paper vigorously denies pulling the story for commercial reasons, and insists it was an editorial decision. Senior figures at the Telegraph have argued privately that Cable's comments about bringing the coalition government down if the Liberal Democrats are "pushed too far" were far more significant than his remarks about a rival media proprietor.

It chose to lead the paper on Cable's assertion in a secretly recorded conversation that: "I have a nuclear option, it's like fighting a war. They know I have nuclear weapons, but I don't have any conventional weapons. If they push me too far then I can walk out of the government and bring the government down, and they know that."

Only a handful of people at the paper knew about the existence of the tapes and management are furious that Cable's comments were handed to rival news organisations. One executive said at the time the paper had been "betrayed".

It is unclear how long the Kroll investigation will last, or who it plans to interview, but it would be unusual if it didn't include the paper's journalists.

Cable has complained to the Press Complaints Commission about the paper's use of "subterfuge".

A spokesman for Telegraph Media Group said it did not comment on internal security matters.